Gas Absorption with Chemical Reactions

Gas absorption is often enhanced by chemical reaction. For instance, acid gases (and ) are usually eliminated from natural gas with absorption using ethanolamine () as a basic solvent.

Consider the absorption of species with a solvent containing a species such as a second-order irreversible chemical reaction, , taking place in the liquid film. Only species is present in the gas phase since has a very low vapor pressure (i.e., is a high boiling component). Species is not present in the bulk liquid since all of reacts with component in the liquid film.

The steady state material balances within the film are given by:

and , where the binary diffusion approximation for and in has been used. These equations simply state that the rates of diffusion of species and are equal to the rate of chemical reaction.

This Demonstration displays the bulk liquid, the gas phase, and the liquid film where the concentrations of species and (blue and red curves, respectively) are shown as a function of position. The user can change the values of the diffusivities, the reaction rate constant, the concentration of in the bulk liquid, as well as the concentration of at the gas-liquid interface.

The displayed flux of species , calculated at the gas-liquid interface, gets larger when the reaction rate is increased. This situation corresponds to a higher uptake of species by the solvent.